Electrolytic capacitor and multi-anodic attachment

ABSTRACT

A multi-anodic aluminum electrolytic capacitor includes an electrical connection to the multiple porous (e.g., tunnel-etched) anodes in an anode stack using a single anode tab that is attached only to a first anode. Other anodes are electrically coupled to the anode tab through the first anode. Anodes in the anode stack are in intimate physical and electrical contact with other such anodes as a result of layering effected by planar stacking or cylindrical winding. The need for separate tabs to different anode layers is eliminated or at least minimized, thereby reducing capacitor volume, increasing capacitor reliability, and reducing the cost and complexity of the capacitor manufacturing process for multi-anodic capacitors. The capacitor is capable of use in implantable defibrillators, camera photoflashes, and other electric circuit applications.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/063,692, filed on Apr. 21, 1998 now U.S. Pat. No. 6,249,423 B1, thespecification of which is incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to capacitors and particularly, but notby way of limitation, to a multi-anodic electrolytic capacitor andattachment to the multiple anodes.

BACKGROUND OF THE INVENTION

Capacitors are electrical components that store electrical energy in anelectromagnetic field between electrodes that are separated by adielectric insulator. Each electrode carries a charge that is oppositein polarity to the charge on the other electrode. Capacitors find manyapplications in a wide variety of electric circuits. Some applicationsrequire the capacitor to withstand a high voltage between itselectrodes. For example, some camera flash devices produce light by anelectric discharge in a gas. A high voltage is required to create thedischarge. A power converter transforms a low voltage obtained from abattery into a high voltage, which is stored on the capacitor and usedto trigger the flash. In another example, external and implantabledefibrillators deliver a high voltage electrical countershock to theheart. The countershock restores the heart's rhythm during cardiacarrhythmias such as life-threatening ventricular fibrillation. In animplantable defibrillator, a power converter transforms a low voltage(e.g., approximately 3.25 Volts), obtained from a battery, into a highvoltage (e.g., approximately 750 Volts), which is stored on capacitorsand used to defibrillate the heart.

Electrolytic capacitors are used in cameras, defibrillators, and forother electric circuit applications. An electrolytic capacitor includestwo electrodes: an anode and a cathode. The dielectric insulator betweenthe anode and cathode is formed by anodizing the anode electrode (i.e.,growing an oxide on the anode). The anode and cathode electrodes arephysically separated from each other by a porous separator that issoaked with a conductive electrolyte solution. The electrolyte acts as apart of the cathode electrode. A parallel plate capacitor is formed by asubstantially parallel planar arrangement of superjacent anode andcathode plates. A separator is interposed in between the anode andcathode electrode plates. A cylindrical capacitor is formed by windinganode, cathode, and separator strips into a spiraled cylindrical roll.For electrically connecting the capacitor in an electric circuit, tabsare joined to the anode and cathode. The tabs protrude outwardly from anend of the cylinder so that the capacitor can be connected in theelectric circuit.

By maximizing the energy density of a capacitor, its volume can bereduced. This is particularly important for implantable medical devices,such as implantable defibrillators, since the defibrillation energystorage capacitor occupies a significant portion of the implantabledefibrillator device. Smaller implantable defibrillator devices aredesired. Smaller defibrillators are easier to implant in a patient.Also, for a particular defibrillator size, a smaller capacitor allowsthe use of a larger battery, which increases the effective usable lifeof the implanted device before surgical replacement is required. Thus,one goal of implantable defibrillator design is to maximize capacitorenergy density and minimize capacitor volume.

The energy density of a capacitor increases in proportion to acorresponding increase in the surface area of the anode. For example, ananode having a particular macroscopic surface area can be roughened toincrease its microscopic surface area. The capacitance per unit ofmacroscopic surface area, which is sometime referred to as the foil gainof the capacitor, increases as a result of roughening techniques. Onesuch roughening technique includes tunnel etching tiny openingspartially or completely through the anode electrode strip.

Anode surface area is further increased by stacking multipletunnel-etched anodes, thereby obtaining even more surface area and, inturn, an even capacitance per unit area of the anode stack. However, insuch multi-anodic capacitors, an electrical connection to each anode inthe stack is still required. One approach to making an electricalconnection to each anode in the stack is to join a connecting tab toeach anode. Individually joining such tabs to each anode, however,increases the volume of the capacitor. Cylindrical capacitors, forexample, will bulge as a result of each tab that is inserted into theroll and joined to an anode strip. Not only does this disadvantageouslyincrease the capacitor volume, it increases reliability concerns.Joining tabs to the anode strips causes mechanical stresses, such as atthe joints between the tab and the anode strip, and within the anodestrip near the edges of the tab. Tunnel-etched anode strips areextremely brittle, making the anodes highly susceptible to suchmechanical stresses. Thus, significant disadvantages arise fromproviding separate tabs to individually contact each anode strip.

Capacitor volume can be reduced slightly by interposing a shared tab inbetween two adjacent anode plates in the anode stack, such as describedin Pless et al. U.S. Pat. No. 5,131,388, entitled, “IMPLANTABLE CARDIACDEFIBRILLATOR WITH IMPROVED CAPACITORS.” This technique still requiresat least one tab for every two adjacent anode plates, thereby limitingthe reduction in capacitor volume that is obtained. Even moredisadvantageously, the Pless et al. patent requires that each doubleanode is formed by welding two anode plates together with an aluminumstrip (i.e., a tab) between them for electrical contact. Not only doessuch welding add complexity and expense to the manufacture of thecapacitor, it causes reliability concerns because the extremely brittletunnel etched anodes may be further weakened by the welding process. Theprocess of joining anode plates by welding is also described in Elias etal. U.S. Pat. No. 5,660,737 entitled “PROCESS FOR MAKING A CAPACITORFOIL WITH ENHANCED SURFACE AREA,” in which each anode plate must have anelectrical connection to the anode terminal, and the anode plates arejoined to each other and a tab connection by welding.

Another example of a multi-anodic capacitor is described in MacFarlaneet al. U.S. Pat. No. 5,584,890 entitled “METHODS OF MAKING MULTIPLEANODE CAPACITORS.” MacFarlane et al. describes a triple layer anodestack in which an opening in the intermediate anode layer receives aninserted tab that is shared between the adjacent three anodes, each ofwhich must contact the tab. This technique still requires at least onetab for every three adjacent anode plates, thereby limiting thereduction in capacitor volume that is obtained. Even moredisadvantageously, the MacFarlane et al. patent requires that eachtriple anode stack is formed by joining the three anode plates togetherusing cold welding, laser welding, or arc welding, even though, asrecognized by MacFarlane et al., “highly etched oxidized anode foil isbrittle and difficult to join.”

Thus, there is a need for further reducing capacitor volume, increasingcapacitor reliability, and reducing cost and complexity of the capacitormanufacturing process, for multi-anodic capacitors used in implantabledefibrillators, camera photoflashes, and other electric circuitapplications.

SUMMARY OF THE INVENTION

The above-mentioned shortcomings, disadvantages and problems areaddressed by the present invention, which will be understood by readingand studying the following specification. The present inventionprovides, among other things, a capacitor. In one embodiment, thecapacitor includes a first anode, a cathode, and a separator between thefirst anode and the cathode. The separator carries an electrolyte. A tabis physically and electrically coupled to the first anode, such as forproviding an external circuit connection. A second anode is physicallyseparated from the tab and electrically coupled to the tab through thefirst anode. The unjoined first and second anodes are electricallyintercoupled by physical contact between the first and second anodes.

Though portions of the invention are described in particular withrespect to first and second anodes in a multi-anode stack, it isunderstood that, in other embodiments, the multi-anode stack includesmore than two anodes.

In various further embodiments, the first and second anodes arephysically and electrically intercoupled by physical contact between thefirst and second anodes at a plurality of points (e.g., distributedthroughout an interface between the first and second anodes). Thecapacitor further comprising a dielectric that includes oxidizedportions of the first anode, or of the first and second anodes. In oneexample, the physical contact between the first and second anodes iseffected by a planar layering of the first and second anodes, such as byarranging the first and second anodes, the separator, and the cathode inan approximately planar and approximately superjacent configuration. Inanother example, the physical contact between the first and secondanodes is effected by a cylindrically wound layering of the first andsecond anodes, such as by winding the first and second anodes, theseparator, and the cathode include strips in an approximatelycylindrical configuration. In one embodiment, at least one of the firstand second anodes is porous (e.g., including tunnel-etched aluminumfoil.)

In a further embodiment, the present invention provides, among otherthings, an implantable cardiac rhythm management system including thecapacitor described above. The system further comprises an implantabledefibrillator carrying the capacitor, and a leadwire that is adapted tobe coupled to a heart for delivering an electrical countershock energythat is stored on the capacitor.

In another embodiment of the present invention, a capacitor includes afirst anode, a cathode, and a separator between the first anode and thecathode. The separator carries a conductive electrolyte. A tab isphysically and electrically coupled to the first anode. A second anodeis physically separated from the tab and electrically coupled to the tabthrough the first anode. A dielectric includes oxide on at least onesurface of the first and second anodes. The dielectric electricallyisolates the first and second anodes from the electrolyte and thecathode. The first and second anodes are physically layered in intimatecontact with each other. This breaks through portions of the oxide onopposing surfaces of the first and second anodes, resulting inelectrical contact between the first and second anodes.

In another embodiment of the present invention, the capacitor includes afirst anode, a cathode, and a separator between the first anode and thecathode. The separator carries a conductive electrolyte. A tab isphysically and electrically coupled to the first anode. The capacitoralso includes a plurality of second anodes. Each second anode isphysically separated from the tab and electrically coupled to the tabthrough the first anode. A dielectric includes oxidized portions of onesof the first and second anodes. The dielectric electrically isolates thefirst and second anodes from the electrolyte and the cathode. Theunjoined first and second anodes are physically and electricallyintercoupled by physical contact between the first and second anodes.

In various further embodiments, the first and second anodes arephysically layered in intimate contact with each other. This breaksthrough portions of the oxide on opposing surfaces of the first andsecond anodes, resulting in electrical contact between the first andsecond anodes.

In another embodiment, the present invention includes a method offorming a capacitor. The method includes disposing a separator between afirst anode and a cathode. The separator carries a conductiveelectrolyte. A tab is physically and electrically coupled to the firstanode. A second anode is disposed to be physically separated from thetab. A second anode is electrically coupled to the tab through the firstanode by physically contacting the unjoined first and second electrodes.

In various further embodiments, the method includes, for example,further including arranging the first and second anodes, the separator,and the cathode in an approximately planar and approximately superacentconfiguration. In another example, the method further includes windingstrips of the first and second anodes, the separator, and the cathode inan approximately cylindrical configuration. In one embodiment,electrically coupling a second anode to the tab through the first anodeincludes physically layering the first and second anodes in intimatecontact with each other, thereby breaking through portions of the oxideon opposing surfaces of the first and second anodes and resulting inelectrical contact between the first and second anodes.

Thus, the present invention provides, among other things, a multi-anodicelectrolytic capacitor and electrical connection to the multiple anodesin an anode stack using a single anode tab that is attached only to afirst anode. Other anodes are electrically coupled to the anode tabthrough the first anode. Anodes in the anode stack are in intimatephysical and electrical contact with other such anodes.

The present invention reduces capacitor volume, increases capacitorreliability, and reduces the cost and complexity of the capacitormanufacturing process for multi-anodic capacitors. The present inventionis capable of use in implantable defibrillators, camera photoflashes,and other electric circuit applications. Other advantages will becomeapparent upon reading the following detailed description of theinvention and viewing the accompanying drawings that form a partthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like numerals describe substantially similar componentsthroughout the several views. Shapes and dimensions are not criticalunless indicated as such in the drawing or the accompanying detaileddescription of the invention.

FIG. 1 is a schematic/block diagram illustrating generally oneembodiment of a cardiac rhythm management system according to one aspectof the present invention.

FIG. 2A illustrates generally one embodiment of a cylindrical capacitor.

FIG. 2B illustrates generally one embodiment of partially unrolledportions of a cylindrical electrolytic capacitor.

FIG. 3 is a cross-sectional view that illustrates generally oneembodiment of portions of a capacitor.

FIG. 4 is a cross-sectional view that illustrates generally oneembodiment of an unrolled portion of a capacitor.

FIG. 5 is a cross-sectional view that illustrates generally anotherembodiment of an unrolled portion of a capacitor.

FIG. 6 is a cross-sectional view that illustrates generally anotherembodiment of an unrolled portion of a capacitor.

FIG. 7 is a cross-sectional view that illustrates generally anotherembodiment of an unrolled portion of a capacitor.

FIG. 8 is a schematic diagram that illustrates generally one embodimentof a planar capacitor.

FIG. 9 is a schematic diagram that illustrates generally, by way ofexample, but not by way of limitation, one embodiment of a planarcapacitor element.

FIG. 10 is a schematic diagram that illustrates generally anotherembodiment of a planar capacitor element.

FIG. 11 is a schematic diagram that illustrates generally an embodimentof a planar capacitor element in which anode tabs and cathode tabs areinserted into the capacitor element.

FIG. 12 is a schematic diagram that illustrates generally one embodimentof a capacitor winder apparatus.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the scope of the presentinvention. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of the present invention isdefined by the appended claims and their equivalents.

The present invention provides, among other things, a multi-anodicelectrolytic capacitor and attachment to the multiple anodes. Thepresent invention reduces capacitor volume, increases capacitorreliability, and reduces the cost and complexity of the capacitormanufacturing process for multi-anodic capacitors. The present inventionis capable of use in implantable defibrillators, camera photoflashes,and other electric circuit applications, as will become apparent byreading the following detailed description of the invention and viewingthe accompanying drawings which form a part thereof.

FIG. 1 is a schematic/block diagram illustrating generally, by way ofexample, but not by way of limitation, one embodiment of a cardiacrhythm management system 100 according to one aspect of the presentinvention. System 100 includes, among other things, cardiac rhythmmanagement device 105 and leadwire (“lead”) 110 for communicatingsignals between device 105 and a portion of a living organism, such asheart 115. In the illustrated example, device 105 includes an automaticimplantable cardioverter/defibrillator (AICD), but any other apparatusfor cardiac rhythm management is also included within the presentinvention.

In the illustrated embodiment, portions of system 100 is implantable inthe living organism, such as in a pectoral or abdominal region of ahuman patient, or elsewhere. In another embodiment, portions of system100 (e.g., device 105) are alternatively disposed externally to thehuman patient. In the illustrated embodiment, portions of lead 110 aredisposed in the right ventricle, however, any other positioning of lead110 is included within the present invention. In one embodiment, lead110 is a commercially available endocardial defibrillation lead. System100 can also include other leads in addition to lead 110, appropriatelydisposed, such as in or around heart 115, or elsewhere.

In one example, a first conductor of multiconductor lead 110electrically couples a first electrode 120 to device 105. A secondconductor of multiconductor lead 110 independently electrically couplesa second electrode 125 to device 105. Device 105 includes an energysource, such as battery 130, a power converter 135, such as a flybackconverter, at least one defibrillation output capacitor 140, and acontroller 145 for controlling the operation of device 105. In oneembodiment, power converter 135 transforms the terminal voltage ofbattery 130, which is approximately between 2 Volts and 3.25 Volts, intoan approximately 700-800 Volt (maximum) defibrillation output energypulse stored on the defibrillation output capacitor 140. In anotherembodiment, power converter 135 transforms the terminal voltage of twoseries-coupled batteries, which is approximately between 4 Volts and6.25 Volts, into the approximately 700-800 Volt (maximum) defibrillationoutput energy pulse stored on the defibrillation output capacitor 140.In particular modes of operation, lesser defibillation output energiesand voltages are delivered (e.g., defibrillation output energies thatare approximately between 0.1-40 Joules, and defibrillation outputvoltages that range approximately between 10-800 Volts).

FIG. 2A illustrates generally, by way of example, but not by way oflimitation, one embodiment of a cylindrical capacitor 140. In oneembodiment, capacitor 140 includes a case 200 for carrying, enclosing,or sealing a spirally wound aluminum electrolytic capacitor, asdescribed below. Anode connection tab 205 and cathode connection tab 210provide electrical access to respective anode and cathode terminals ofcapacitor 140, as described below.

FIG. 2B illustrates generally, by way of example, but not by way oflimitation, one embodiment of a partially unrolled portion of acylindrical aluminum electrolytic capacitor 140. Anode connection tab205 physically and electrically contacts portions of at least one anodeof multiple anode stack 215, which is a ribbon or strip that forms afirst electrode of capacitor 140. Cathode connection tab 210 physicallyand electrically contacts portions of cathode 220, which is a ribbon orstrip that forms a second electrode of capacitor 140. One or moreseparators 225 on each side of cathode 220 provides physical separationbetween cathode 220 and anode stack 215 when spirally rolled up togetherinto a cylindrically shaped capacitor 140. In one embodiment, each ofseparators 225 includes one or more paper strips. For example, using twopaper strips obtains redundancy that better protects againstanode-to-cathode short-circuits in the event of pinholes in the paperstrips. In one embodiment, permeable separators 225 carry a conductiveelectrolyte that, together with cathode strip 220 and cathode connectiontab 210, forms the second electrode (i.e., a cathode electrode) ofcapacitor 140. However, the present invention is not limited to use onlyin capacitors using a liquid conductive electrolyte.

FIG. 3 is a cross-sectional view that illustrates generally, by way ofexample, but not by way of limitation, one embodiment of portions ofcapacitor 140. Cathode 220 is separated from anode stack 215 byseparators 225A-B. Anode stack 215 includes a stacked configuration ofmultiple anodes, such as first anode 215A, second anode 215B, and thirdanode 215C. In one embodiment, each of anodes 215A-C is a high foil-gaintunnel-etched aluminum foil strip that has been anodized (i.e., a thininsulating aluminum oxide layer has been grown on each surface of eachof the aluminum foil anodes 215A-C). The aluminum oxide layer formed onthird anode 215C provides a capacitor dielectric between third anode215C and the conductive electrolyte carried by separator 225B. Thealuminum oxide layer formed on second anode 215B provides a capacitordielectric between second anode 215B and cathode 220.

According to one aspect of the invention, an anode connection tab 205 isphysically and electrically coupled to first anode 215A, such as bybeing physically joined together by cold welding, swaging, ultrasonic orspot welding, riveting, or any other suitable joining process. Secondanode 215B is physically separated from tab 205, such as by first anode215A, which is interposed in between second anode 215B and tab 205.Second anode 215B is, however, electrically coupled to tab 205 throughfirst anode 215A, to which second anode 215B is physically andelectrically intercoupled, without joining, such as by intimate physicalcontact between first anode 215A and second anode 215B. (In thisapplication, joining is defined as physically uniting, attaching, oraffixing two separate elements into a single mechanically combinedunitary element by welding, including cold welding by stamping, to jointhe two elements together. Unjoined elements are not welded together,but can instead be in intimate physical contact with each other, withoutjoining.) Second anode 215B is unjoined to each of first anode 215A andtab 205.

FIG. 4 is a cross-sectional view that illustrates generally, by way ofexample, but not by way of limitation, one embodiment of an unrolledportion of capacitor 140. FIG. 4 more clearly illustrates the oxide 400on the anodized surfaces of anodes 215A-C. Anode tab 205 is joined toone or both of first anode 215A and third anode 215C, such as describedabove. As discussed above, the starting material for each first anode215A, second anode 215B, and third anode 215C is oxidized on bothsurfaces by anodization. In one embodiment, joining first anode 215A andthird anode 215C to tab 205 breaks through portions of interveninginsulating oxide 400, resulting in physical and electrical contactbetween tab 205 and each of first anode 215A and third anode 215C.

It is believed that a compressive force between first anode 215A andsecond anode 215B breaks through portions of intervening insulatingoxide 400. This is believed to result in intimate physical andelectrical contact between first anode 215A and second anode 215B, suchas at a plurality of points distributed throughout the interface betweenfirst anode 215A and second anode 215B, as illustrated in FIG. 4. Thus,physical contact between first anode 215A and second anode 215B isobtained at unoxidized (e.g., broken through) portions 405 of theinterface between first anode 215A and second anode 215B.

In one embodiment, this intimate physical contact between first anode215A and second anode 215B is obtained from compressive force appliedduring the spiral winding of the constituent strips into the cylindricalcapacitor 140 of FIG. 3. However, other techniques of applyingcompressive force or pressure to break through oxide 400 or otherwiseobtain electrical contact between first anode 215A and second anode 215Bare also included within the invention. In general, enough force shouldbe applied to break through portions of oxide 400 between adjacentanodes in the stacked multi-anode strip 215. The applied force shouldnot be so great as to damage oxide dielectrics 410A-B, which are alsoformed by anodization. Dielectric 410A is in contact with somewhatpliant separator 225B (e.g., comprising gauze fabric or kraft paper).Similarly, dielectric 410B is in contact with somewhat pliant separator225A. In one embodiment, separators 225A-B are sufficiently yielding toprotect against damage to oxide dielectrics 410A-B when force is appliedduring spiral winding or otherwise.

According to one aspect of the invention illustrated in FIG. 4, secondanode 215B, of stacked multi-anode strip 215, need not directly contactanode tab 205. Instead, second anode 215B is electrically coupled toanode tab 205 through first anode 215A. In another embodiment,additional anode layers are added in multi-anode strip 215. Particularones of these additional anode layers need not directly contact anodetab 205. Instead, these additional anode layers are electrically coupledto anode tab 205 through other anode layers in multi-anode strip 215.

FIG. 5 is a cross-sectional view that illustrates generally, by way ofexample, but not by way of limitation, another embodiment of an unrolledportion of capacitor 140. FIG. 5 illustrates a fourth anode 215D inmulti-anode strip 215. In one embodiment, fourth anode 215D electricallycontacts second anode 215B as a result of intimate physical contactbetween fourth anode 215D and second anode 215B, such as obtained by theforce of spirally winding cylindrical capacitor 140, as described above.As a result, fourth anode 215D is electrically coupled to anode tab 205through second anode 215B and first anode 215A.

Further anode layers, beyond those illustrated in FIG. 5, can also beadded. These additional anode layers are similarly electrically coupledto a tab 205 that is not in direct physical contact with such additionalanode layers. The additional anode layers increase the anode surfacearea which, in turn, results in a higher foil gain and an increasedcapacitance per unit volume. A smaller capacitor results. The smallercapacitor advantageously reduces the size of implantable cardiac rhythmmanagement device 105 or, alternatively, allows the use of a biggerbattery to provide increased implanted longevity of device 105.

According to another aspect of the invention, tab 205 is joined only tofirst anode 215A. This avoids the need for joining multiple anodes inanode stack 215A to tab 205. Instead, particular anodes are electricallycoupled to tab 205 through intimate physical contact with other anodes,as described above. Because the tunnel-etched oxidized anodes areextremely brittle, they are difficult to join, as discussed above. Thepresent invention, however, eliminates, or at least minimizes, the needto join anodes to anode tab 205.

FIG. 6 is a cross-sectional view that illustrates generally, by way ofexample, but not by way of limitation, another embodiment of an unrolledportion of capacitor 140. In FIG. 6, multiple anode layers in anodestack 215 are disposed on either side of anode tab 205. For example,first anode 215A and second anode 215B are disposed between anode tab205 and separator 225B. Second anode 215B is physically isolated fromanode tab 205, but is electrically coupled to anode tab 205 throughfirst anode 215A, as described above. Third anode 215C and fourth anode215B are disposed on the opposite side of anode tab 205. Fourth anode215D is physically isolated from anode tab 205, but is electricallycoupled to anode tab 205 through third anode 215C, as described above.

FIG. 7 is a cross-sectional view that illustrates generally, by way ofexample, but not by way of limitation, another embodiment of an unrolledportion of capacitor 140. In FIG. 7, anode stack 215 includes only twoanode layers, such as first anode 215A and second anode 215B. Secondanode 215B is physically isolated from anode tab 205, but iselectrically coupled to anode tab 205 through first anode 215A, asdescribed above.

FIG. 8 is a schematic diagram that illustrates generally, by way ofexample, but not by way of limitation, one embodiment of a planarcapacitor 800. In one embodiment, capacitor 800 includes a multilayercapacitor element 805. Capacitor 800 also includes an apparatus forapplying a compressive force to capacitor element 805. In one example,plates 810A-B are disposed on opposing sides of capacitor element 805.Openings in each of plates 810A-B receive threaded screws 815A-D. Screws815A-D are tightened to obtain the compressive force applied tocapacitor element 805. It is understood that FIG. 8 illustrates but oneexample of many available techniques included within the presentinvention for applying force to capacitor element 805. Many othertechniques (e.g., encasing capacitor element 805) also obtain such acompressive force. In another example, simply placing capacitor element805 in a tight container provides the compressive force to capacitorelement 805.

FIG. 9 is a schematic diagram that illustrates generally, by way ofexample, but not by way of limitation, one embodiment of planarcapacitor element 805. In one embodiment, capacitor element 805 includesa plurality of cells 900A, 900B, . . . , 900N, referred to generally ascells 900. Each of cells 900 includes a cathode 905, a multi-layer anodestack, 910, a separator 915 between a dielectric layer 917 each anodestack 910 and a corresponding substantially adjacent cathode 905, ananode tab 920, and a cathode tab 925. In the embodiment of FIG. 9, eachseparator 915 includes two pieces of liquid electrolyte permeable paper915A-B, and each anode stack 910 includes a first anode 910A, a secondanode 910B, and a third anode 910C.

In FIG. 9, each first anode 910 is joined to an anode tab 920, such asby cold welding, swaging, ultrasonic or spot welding, riveting, or anyother suitable joining process. In one embodiment, second anode 910B andthird anode 910C are each physically isolated from anode tab 920. Secondanode 910B and third anode 910C are electrically coupled to anode tab920 through first anode 910A. Each of second anode 910B and third anode910C are in intimate physical and electrical contact with first anode910A as a result of a compressive force.

In FIG. 9, the starting material for each first anode 910A, second anode910B, and third anode 910C is oxidized on both surfaces by anodization,as discussed above. However, it is believed that the applied compressiveforce breaks through portions of the insulating surface oxide betweenfirst anode 910A and second anode 910B, and between first anode 910A andthird anode 910C. This is believed to result in intimate physical andelectrical contact between first anode 910A and each of second anode910B and third anode 910C, as discussed above. The applied force shouldnot be so great as to damage oxide dielectrics 917, which are alsoformed by anodization of the surfaces of the anode starting material. Inone embodiment, separators 915 (e.g., comprising gauze fabric or kraftpaper) are sufficiently yielding to protect against damage to oxidedielectrics 917 when the compressive force is applied.

FIG. 10 is a schematic diagram that illustrates generally, by way ofexample, but not by way of limitation, another embodiment of planarcapacitor element 805. In FIG. 10, anode tabs 920 are joined to firstanodes 910, such as described above. Cathode tabs 925 are joined tocathodes 905, such as also described above. Anode tabs 920 are alsojoined together for providing an external anode connection. Similarly,cathode tabs 925 are joined together for providing an external cathodeconnection.

In the embodiments of FIGS. 9 and 10, each anode tab 920 need only bejoined to a single anode (e.g., first anode 910A). This is advantageousbecause the tunnel-etched anodes are brittle, making the joining processdifficult. Some anode materials may be so brittle that joining the anodetab 920 to an overhanging portion of the first anode, as illustrated inFIGS. 9 and 10, is very difficult. As an alternative, anode tab 920 isinserted into anode stack 910 as illustrated in FIG. 11.

FIG. 11 is a schematic diagram that illustrates generally, by way ofexample, but not by way of limitation, an embodiment of capacitorelement 805 in which anode tabs 920 and cathode tabs 925 are insertedinto the capacitor element 805. In one example, each anode tab 920 isinserted into an anode stack 910, and joined to first anode 910A, secondanode 910B, or both, such as described above. Each cathode tab 925 isalso inserted into capacitor element 805 and joined to a cathode 925.Each third anode 910C is physically isolated from the correspondinganode tab 920. Each third anode 910C is electrically coupled to anodetab 920 through first anode 910A. Intimate physical and electricalcontact between third anode 910C and first anode 910A results from theapplied compressive force, as described above, which breaks throughportions of the intervening surface oxide, as described above.

Example Method of Forming Cylindrical Capacitor

FIGS. 2 through 7 illustrate various embodiments of portions of thepresent invention providing a cylindrical capacitor 140, as discussedabove. In one example, the cylindrical capacitor 140 is formed by spiralwinding using a capacitor winder apparatus. FIG. 12 is a schematicdiagram that illustrates generally one example embodiment of such acapacitor winder 1200. In FIG. 12, capacitor winder 1200 is a Model 820dual anode lug capacitor winder available from Micro Tech Manufacturing,Inc. of Worcester, Mass. As illustrated, the capacitor winder 1200 iscapable of forming a cylindrical capacitor 140 having only 2 anodes inanode stack 215. In one embodiment of the present invention, an anodestack 215 having 2 anodes is provided. However, as discussed above,certain embodiments of the present invention utilize more than 2 anodesin anode stack 215. According to one technique of making one embodimentof the present invention, additional anode strips are trimmed to size,and the trimmed anode strips are manually inserted between the dualanode ribbons that are fed by reels on capacitor winder 1200. Thisprovides an anode stack 215, which includes more than two anodes, in theresulting cylindrically wound capacitor 140. Alternatively, capacitorwinder 1200 can be modified. Additional reels and feeders can be addedto supply the additional anode ribbons for forming a capacitor 140having an anode stack 215 that includes more than 2 anodes.

In one embodiment, by way of example, but not by way of limitation, theanode stack 215 includes 3 anode layers 215A-C (as illustrated in FIG.4). Each one of anode layers 215A-C formed of a tunnel-etched oxidizedaluminum foil ribbon having a width of approximately 24 millimeters anda thickness of approximately 0.0041 inches. The cathode 220 is formedfrom an aluminum foil ribbon having a width of approximately 24millimeters and a thickness of approximately 0.0012 inches. Eachseparator 225A and 225B includes two layers of a paper ribbon, eachhaving a width of 27 millimeters and a thickness of approximatelybetween 12.7 and 20 microns. Anode stack 215, cathode 220, and paperseparators 225A-B are cut to a desired length to obtain a particularcapacitance value of capacitor 140. In one embodiment, the woundcapacitor 140 has a cylindrical diameter of approximately 14.5millimeters, and is held together (i.e., prevented from unwinding) bywrapping in an adhesive tape having a width of approximately 26.6microns and a thickness of approximately 53 microns.

As described above, it is believed that compressive force (e.g., as aresult of the cylindrical winding) results in intimate physical andelectrical contact between anodes in anode stack 215, such that anodetab 205 need only be joined to a single anode in anode stack 215 forobtaining an electrical connection to other anodes in anode stack 215.For the above-described example, one embodiment of settings used on theModel 820 dual anode lug capacitor winder to obtain intimate physicaland electrical contact between first anode 215A and second anode 215B asa result of compressive force is illustrated, by way of example, but notby way of limitation, in Table 1. While the settings set forth in Table1 will enable one skilled in the art to make and use certain embodimentsof the invention, it is understood that other settings may also be used.

TABLE 1 Exemplary settings for Model 820 Capacitor Winder ParameterSetting Paper Tension 6.0 Anode Tension 1.5 Cathode Tension 4.5

CONCLUSION

Thus, the present invention provides, among other things, a multi-anodicelectrolytic capacitor and electrical connection to the multiple anodesin an anode stack using a single anode tab that is attached only to afirst anode. Other anodes are electrically coupled to the anode tabthrough the first anode. Anodes in the anode stack are in intimatephysical and electrical contact with other such anodes.

The present invention reduces capacitor volume, increases capacitorreliability, and reduces the cost and complexity of the capacitormanufacturing process for multi-anodic capacitors. The present inventionis capable of use in implantable defibrillators, camera photoflashes,and other electric circuit applications.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. A planar capacitor comprising: a planar casehaving first and second opposing and substantially planar surfaces; oneor more anode stacks between the first and second planar surfaces, withat least one of the anode stacks comprising: an inner anode layerbetween first and second outer anode layers, with each outer layerhaving an inner surface facing the inner anode layer and an outersurface facing away from the inner anode layer; and only one tabextending from the at least one anode stack, the one tab having twomajor opposing surfaces, with at least one of the two major surfacescontacting the outer surface of the first or second outer anode layer.2. The capacitor of claim 1, wherein the at least one anode stackincludes no more than three anode layers.
 3. The capacitor of claim 1,wherein at least one of the anode layers comprises a tunnel-etched foil.4. The capacitor of claim 1, wherein at least one of the anode layerscomprises a porous foil.
 5. The capacitor of claim 1, wherein the tabcomprises a rectangular strip of conductive metal.
 6. The capacitor ofclaim 1, further comprising: at least one cathode; and at least oneseparator between the at least one anode stack and the one cathode, theone separator including a liquid electrolyte.
 7. An implantable cardiacrhythm management system comprising the capacitor of claim
 1. 8. Aplanar capacitor comprising: a planar case having first and secondopposing and substantially planar surfaces; at least one anode stackbetween the first and second planar surfaces, the one anode stack havinga total thickness and comprising: an inner anode layer between first andsecond outer anode layers, with each outer layer having an inner surfacefacing the inner anode layer and an outer surface facing away from theinner anode layer and with each anode layer having a respective layerthickness; and only one tab extending from the one anode stack, the onetab having two major opposing surfaces defining a tab thickness, with atleast one of the two major surfaces contacting the inner surface of thefirst or second outer anode layer and with the total thickness being atleast as great as a sum of the layer thicknesses of the anode layers andthe tab thickness.
 9. The capacitor of claim 8, wherein the one anodestack includes no more than three anode layers.
 10. The capacitor ofclaim 8, wherein at least one of the anode layers comprises atunnel-etched foil, and wherein none of the anode layers are joined toany other anode layer in the one anode stack.
 11. The capacitor of claim8, wherein the one tab comprises a rectangular strip of conductivemetal.
 12. The capacitor of claim 8, further comprising: at least onecathode; and at least one separator between the one anode stack and theone cathode, the one separator including an electrolyte.
 13. Animplantable cardiac rhythm management system comprising the capacitor ofclaim
 8. 14. A planar capacitor comprising: a planar case having firstand second opposing and substantially planar surfaces; and at least oneanode stack between the first and second planar surfaces, the one anodestack including: two or more anode layers, with at least one of theanode layers not joined to any other anode layer; and no more than onetab extending from the one anode stack for every two of the anode layersin the one anode stack, with the one tab having a tab thicknesscontributing to the total thickness of the one anode stack.